1. Field of the Invention
The present invention relates to a method for manufacturing a precursor wire used for the manufacture of a carbon-fiber-reinforced metal composite material.
2. Description of the Related Art
A carbon-fiber-reinforced metal composite materials (CFRM) composing of carbon fibers as a reinforcement and a metal as a matrix, especially such as aluminum, magnesium, or an alloy thereof for the matrix, has excellent heat resistance and thermal conductivity, and are particularly high in specific strength and specific modulus. Therefore, these materials are considered to be promising for using in various fields of application, particularly for aerospace application.
The CFRM may be manufactured by several methods. In one of these methods, continuous fiber bundles of carbon filaments are introduced into a molten metal to be impregnated with the molten metal, and are drawn up, whereupon the molten metal is solidified to provide precursor wires. These precursor wires are arranged in order in one direction, for example, and are joined together, for example, into a plate and a tube by means of a hot press or the like.
Intrinsically, however, the carbon fibers are not easy to be wet with a molten metal, so that it is very difficult to manufacture high-performance precursor wires or CFRM. Accordingly, methods for improving the wettability between carbon fibers and a molten metal have been studied for long time.
A method for improving the wettability is described in U.S. Pat. Nos. 3,860,443 and 3,894,863 and their supposed Japanese version, Examined Japanese Patent Publication No. 59-12733. According to this method, a layer of titanium boride or of a mixture of titanium boride and titanium carbide is formed on the surface of each carbon filament by chemical vapor deposition (CVD process) in which a mixture of gaseous compounds of titanium and boron is reduced on the filament surface. In U.S. Pat. Nos. 4,082,864 and 4,145,471, moreover, is mentioned that if a layer of metallic boride in thickness of submicron orders is formed on the carbon filaments by the CVD process, the boride layer serves to restrain the reaction between the filaments and a metal matrix, thereby ensuring strong mechanical adhesion between them. In U.S. Pat. No. 4,223,075, furthermore, is mentioned that a titanium-boron coating on carbon fibers can be effectively restrained from diffusing into a molten matrix metal, when the carbon fibers are dipped into the molten metal, by previously adding titanium and boron, as alloy elements, to the matrix metal. Further, "Failure Modes in Composites" IV, page 301 in A publication of The Metallurgical Society of AIME, 1979, has a description that a sizing agent adhering to carbon fibers must be removed before the CVD process, in the aforesaid method. As is generally known, the sizing agent is used to bind a continuous fiber bundle consisting single carbon filaments, thereby improving the handling properties of the fiber bundle. Conventionally, epoxy resin is used as the sizing agent.
If the aforementioned conventional method is executed under given conditions, however, the wettability cannot always be satisfactorily improved, and the state of impregnation into the continuous fiber bundle with the molten metal varies depending on the direction, widthwise or lengthwise, of the bundle. Thus, it is very difficult to manufacture precursor wires with good uniformity even if much effort is made.